In recent years, 3D movies of a binocular disparity type have been rapidly spread, which provide right and left eyes of viewers with different images so that the viewers recognize the three-dimensional effect. Showing 3D movies at theaters and watching 3D movies at home with 3D enabled devices are becoming common.
The 3D enabled devices for watching 3D movies at home usually employ liquid crystal shutter glasses. With the liquid crystal shutter glasses, right and left images are alternately displayed on a display (i.e., frame sequential display). A viewer wears the liquid crystal shutter glasses, which shut images coming into the right or left eye in synchronization with the display of an image. This allows the viewer to recognize the right image with the right eye, and the left image with the left eye. As a result, the viewer perceives the three-dimensional effect created by the binocular disparity between the right and left images.
In general, while movies are filmed at a frame frequency of 24 Hz, they are displayed at a frame frequency of 60 Hz under the NTSC system on home television sets. When a two-dimensional video image of 24 Hz is converted to a video image of 60 Hz, frame frequency conversion (i.e., telecine conversion) by 3:2 pull-down may be performed. In the 3:2 pull-down, a single frame of 24 Hz may be alternately displayed as three frames and two frames of 60 Hz.
FIG. 7 illustrates an example where a ball crossing a screen is filmed at 24 Hz and displayed at 60 Hz after performing 3:2 pull-down. As shown, in 3:2 pull-down, the first frame of 24 Hz is displayed as three frames, the second frame of 24 Hz is displayed as two frames, and the third frame of 24 Hz is displayed as three frames. When a human views something moving uniformly like in this example, it is known that the line of sight moves so as to follow the motion.
FIG. 8 illustrates the relationship between time and the display position of the ball shown in FIG. 7. As shown in FIG. 8, the line of sight follows the displayed ball and moves along the track of the line of sight indicated by the arrow. In the graph, while the position of the ball coincides with the track of the line of sight on frames 2 and 7, the position of the ball does not coincide with the track of the line of sight on the other frames. For example, the ball appears behind the track of the line of sight on frames 1, 4, and 6, and appears in front of the track of line of sight on frames 3, 5, and 8. As such, the uniformly moving ball seems to blur back and forth. This state is called a film judder, which can largely influence the image quality in a stereoscopic video image. An example will be described where the right and left images of the scene of FIG. 7 are filmed in 3D at 24 Hz.
FIG. 9 illustrates the relationship between time and the display position of the ball where a stereoscopic video image of 24 Hz is converted to right and left video images of 60 Hz by 3:2 pull-down and displayed by frame sequential display at 120 Hz.
FIG. 10 illustrates deviation of the display position of the ball from the centers of the lines of sight from the right and left eyes and the binocular disparity caused by the deviation. As shown, when a stereoscopic video image of 24 Hz is converted to a stereoscopic video image of 60 Hz by 3:2 pull-down and displayed by frame sequential display at 120 Hz, the degree of the binocular disparity of an output image non-uniformly fluctuates in a range between N−⅖ V and N+⅗ V, where a degree of the binocular disparity between the right and left images of an input image is N, and the movement amount of the input image between frames is V.
With respect to a stereoscopic video image of the binocular disparity type, a viewer recognizes the three-dimensional effect based on the degree of the binocular disparity. If the degree of the binocular disparity non-uniformly fluctuates between the frames due to film judder as shown in FIG. 10, the viewer cannot precisely recognize the three-dimensional effect. In addition, the viewer is forced to three-dimensionally see a hard-to-see image, which could cause eyestrain.
Accordingly, there is a need for a stereoscopic video processing system, which can reduce such deterioration in the image quality caused by 3:2 pull-down.